The objective of this research is an elucidation of the excited electronic states and their radiative and radiationless decay of ethidium bromide and its complex with DNA sufficient to understand the 20-fold fluorescence enhancement observed for the complex compared to aqueous solutions. This knowledge will be applied to the design of analogs of ethidium and to the development of fluorescence methods which will increase the sensitivity of the dye-buoyant density method for the isolation and detection of closed circular DNA. The separation between the closed and open DNA's in the buoyant system as a function of the nature of the ethidium analog will be investigated in an attempt to improve the physical resolution of the species. Binding isotherms for ethidium analogs will be measured in order to determine the binding constants, bound dye interactions and degree of unwinding of the helix. The spectroscopic investigation will include absorption measurements at room temperature and 77 degrees K in various solvents, fluorescence polarization measurements as a function of the energy of the exciting light, phosphorescence detection, triplet-triplet polarized absorption, quantum yield and lifetime measurements, an investigation of deuterium and heavy atom solvent effects, circular dichroism and magnetic circular dichroism measurements and a comparative study of the properties of several analogs of ethidium. Preparative equilibrium centrifugation using PM2 DNA will be used to study the dye buoyant density system. Equilibrium dialysis and solvent partition studies will be used to measure dye binding isotherms to closed and open circular DNA's. Further analogs of ethidium will be synthesized.